The objective of the research outlined in this proposal is to establish the role of the mitochondrial permeability transition (MPT) in the selective vulnerability of neural cells to the effects of dinitrobenzene exposure. Dinitrobenzene (DNB) is widely used as an industrial intermediate in the manufacture of dyes, plastics, and explosives, and induces brain stem glio- vascular lesions in nuclei with high energy requirements. Mitochondria are thought to be a primary target for DNB-induced oxidative stress and differences in the extent of mitochondrial dysfunction may partially explain the selective vulnerability of CNS cells to the neurotoxic effects of DNB exposure. The following aims are proposed to determine the basis for the differential sensitivity of neurons and astrocytes to mitochondrial dysfunction resulting from DNB exposure: (1) Evaluate the capacity of DNB exposure to induce mitochondrial permeability transition (MPT) in cultured neurons and astrocytes; (2) Determine the extent to which changes in cellular redox potential and the subcellular distribution of reduced pyridine nucleotides (NADH/NADPH) and glutathione (GSH) correlate with sensitivity to MPT in primary neurons and astrocytes exposed to DNB; and (3) Determine whether constitutive or inducible expression of of Bcl-2 and Bcl-XL influences sensitivity to MPT in primary neurons and astrocytes and establish the relative potency of Bcl-2 and Bcl-XL to protect against DNB-induced MPT in isolated mitochondria. To test these hypotheses, neurons and astrocytes in primary culture will be evaluated by laser scanning confocal microscopy for evidence of MPT following exposure to DNB. Studies designed to determine the basis for any observed differences in sensitivity to MPT will evaluate the effects of DNB exposure on cellular redox potential and the ability of anti- apoptotic Bcl-2-family proteins to protect against DNB-induced MPT.